We present a methodology to perform fine-grained cycle-accurate timing measurements crossing the user-kernel boundary. Special attention is payed not to deteriorate the results by the measurement process itself. Next, we apply our methodology to obtain execution timing for the system entry and exit paths on x86-based Linux systems. We compare and evaluate three different mechanisms, namely interrupts, call gates and the sysenter/sysexit facility. The measurements are performed on different processor platforms ranging from simple Intel Pentium to Pentium 4 with Hyper Threading and an Intel Itanium system. Our results indicate that timing for kernel entry and exit varies in a non-trivial way. Of the tested architectures, the AMD Athlon exhibits the most efficient behavior.

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